Complex software products are often extensively tested before being released to ensure their performance, stability, and compatibility with other software. However, even after intensive testing, some bugs will inevitably remain in the software products at the time of release. Also, it may not be possible to detect platform specific issues and compatibility issues that can only become apparent after installation.
To address issues associated with software products after they have been released, updates, such as patches, may be provided to customers to resolve these issues. Software patches may be classified into two categories: private patches and public patches. A private patch may be provided by the software developer to one or a few particular customers that are working with the developer on a particular urgent problem associated specifically to the particular customers. Typically, the private patch is tested to make sure that the problem is fixed and is provided to the customers in an expedited manner. Because of the short turnaround time, comprehensive testing often cannot be done. In contrast, a public patch typically addresses issues with a software product that affects most or all customers. These issues may involve security, data corruption issues, or the like. Generally, software developer broadly distributes a public patch and encourages all customers to install the patch. Public patches usually take months to ship and are tested more thoroughly since the patches have a much broader customer impact.
Patching typically involves a linear progression of the product over time. The progression is linear because there is a single branch that holds the product build system, such as sources, data and tools, for the released product. Particularly, a new public patch to a software product typically contains the contents of all previous released private and public patches. Updating software products with a linear progression model may cause problems for customers. For example, customers that install a public patch may have to assume the risk of having new issues caused by previously released private patches that are particularly designed to solve specific issues on another customer's system. Also, the software product installed on the customers' systems may be highly tuned to attain optimal efficiency. Installing a public patch with unnecessary modifications may substantially degrade the performance of the software product.